In a wireless local area network standard, a carrier sense multi-access/collision avoidance (CSMA/CA) technology is used as a channel access method, for example, in a Wireless Fidelity (WiFi) system. Carrier sense is mainly used to determine whether a channel is in an available state. The 802.11 standard includes two carrier sense functions: physical carrier sense and virtual carrier sense.
Compared with a traditional WiFi system, in a next-generation WiFi system, to meet a requirement for a higher rate (dozens of Gb/s), spectrum resources need to be used more efficiently, and technologies such as orthogonal frequency division multiple access (OFDMA) based on a central scheduling mechanism, carrier aggregation, and interference management are used. Although a current channel access mechanism in the wireless local area network standard has taken the physical carrier sense and the virtual carrier sense into consideration, the mechanism cannot adapt to an OFDMA system that has a fixed frame structure and is based on central scheduling. Because in the OFDMA system based on central scheduling, if during downlink sending of a transmission opportunity (TXOP), a channel is obtained by means of competition by a device that supports the traditional WiFi system, subsequent uplink sending may be interfered with by the device that supports the traditional WiFi system and that obtains the channel by means of competition; or if during uplink sending of a TXOP, a channel is obtained by means of competition by a device that supports the traditional WiFi system, subsequent uplink sending and/or downlink sending may be interfered with by the device that supports the traditional WiFi system and that obtains the channel by means of competition. It can be seen that, based on the current channel access mechanism, the next-generation WiFi system is difficult to coexist with the traditional WiFi system. Therefore, a new channel access mechanism is needed to implement coexistence of the next-generation WiFi system with the traditional WiFi system.